Erythropoietin (EPO) is a glycoprotein hormone produced by the kidney in response to tissue hypoxia that stimulates red blood cell production in the bone marrow. The gene for erythropoietin has been cloned and expressed in Chinese hamster ovary (CHO) cells as described in U.S. Pat. No. 4,703,008. Recombinant human erythropoietin (r-HuEPO or Epoetin alfa) has an amino acid sequence identical to that of human urinary erythropoietin, and the two are indistinguishable in chemical, physical and immunological tests. Recombinant human erythropoietin acts by increasing the number of cells capable of differentiating into mature erythrocytes, triggering their differentiation and augmenting hemoglobin synthesis in developing erythroblasts (Krantz S B. Blood (1991) 77: 419–434, Beckman B S, Mason-Garcia M. The Faseb Journal (1991) 5: 2958–2964).
Epoetin alfa has been well tolerated in studies conducted to date. Hypertensive encephalopathy and seizures have occasionally been described in dialysis patients treated with Epoetin alfa, particularly during the early phase of therapy when hematocrit is rising. (Eschbach J W, Egrie J C, Downing M R, Browne J K, Adamson J W. New Engl J Med (1987) 316: 73–78, Winearls C G, Oliver D O, Pippard M J, et al. Lancet (1986) 2 (8517): 1175–1177). Such reports became more rare as experience of use of the compound developed. Occasionally, cancer patients treated with Epoetin alfa have experienced an increase in blood pressure associated with a significant increase in hematocrit. The risk, however, appears substantially lower than in chronic renal failure patients.
No antibody titers against Epoetin alfa could be demonstrated and confirmed in subjects treated with Epoetin alfa for up to 2 years, indicating the absence of immunological sensitivity to Epoetin alfa. Skin rashes and urticaria have been observed rarely and when reported have been mild and transient in nature, but these events suggest allergic hypersensitivity to some components of the Epoetin alfa formulation.
Epoetin alfa is approved for sale in many countries for the treatment of anemia in chronic renal failure (dialysis and predialysis), anemia in zidovudine treated HIV positive patients (US), anemia in cancer patients receiving platinum-based chemotherapy, as a facilitator of autologous blood pre-donation, and as a peri-surgical adjuvant to reduce the likelihood of requiring allogeneic blood transfusions in patients undergoing orthopedic surgery.
EPO influences neuronal stem cells, likely during embryonic development, and possibly during in vitro experiments of differentiation. (Juul et al Pediatr Dev Pathol (1999) 2(2) 148–158. Juul et al Pediatr Res (1998) 43(1) 40–49.) Further, neonates and infants that suffer CNS injury via hypoxia, meningitis, and intraventricular hemorrhage, show an EPO induced neuroprotective effect (Juul et al Ped Res (1999) 46(5) 543–547.)
EPO helps prevent apoptosis of neural tissue in cases of injury that create hypoxia. This may be the result of EPO produced locally by astrocytes (Morishita et al Neuroscience (1996) 76(1) 105–116). Neuroprotection has been demonstrated in gerbil hippocampal and rat cerebrocortical tissue (Sakanaka et al PNAS (1998) 95(8) 4635–4640. Sadamoto et al Biochem Biophys Res Commun (1998) 253(1) 26–32).
EPO induces biological effects of PC12 cells, including changes in Ca2+, changes in membrane potential, and promotion of neuronal survival. This has been interpreted that EPO can stimulate neural function and viability (Koshimura et al J. Neurochem (1999) 72(6) 2565–2572. Tabria et al Int J Dev Neurosci (1995) 13(3/4) 241–252.).
O'Brien et al propose that a 17 amino acid peptide sequence of EPO can act through the EPO-R (Erythropoietin receptor) to induce biological activity in NS20Y, SK-N-MC, and PC12 cells, which includes sprouting, differentiation and neuroprotection. Curiously this peptide does not promote proliferation of hematologic cells, thus it appears inactive in cell lines well understood for their sensitivity to EPO activity. (Campana et al Int J Mol Med (1998) 1(1) 235–241 and U.S. Pat. Nos. 5,700,909, issued on Dec. 23, 1999, 5,571,787, issued on Nov. 5, 1996, 5,714,459, issued on Feb. 3, 1998, and 5,696,080, issued on Dec. 9, 1997, all to O'Brien et al.)
EPO may influence neuronal stem cell commitment to drive differentiation of neurons as opposed to astrocytes or oligodendrocytes. This is compared to a similar activity of EPO, where it functions to drive commitment of hematopoietic stem cells to produce red blood cells (RBCs). There is an apparent relationship between CNS hypoxic injury, resulting in the production of EPO from astrocytes that commits neuronal stem cells to differentiate into neurons, while simultaneously acting as a neuroprotective function for existing neurons. (WIPO publication number WO99/21966, published on May 6, 1999, Weiss et al.)